Reliable navigation systems have always been essential for estimating both distance traveled and position. Some of the earliest type of navigation systems relied upon navigation by stars, or celestial navigation. Prior to the development of celestial navigation, navigation was done by “deduced” (or “dead”) reckoning. In dead-reckoning, the navigator finds his position by measuring the course and distance he has moved from some known point. Starting from a known point the navigator measures out his course and distance from that point. Each ending position would be the starting point for the next course-and-distance measurement.
In order for this method to work, the navigator needs a way to measure his course, and a way to measure the distance moved. Course is typically measured by a magnetic compass, although other methods, such as a heading gyroscope, could also be used. Distance is determined by a time and speed calculation: the navigator multiplied the speed of travel by the time traveled to get the distance. For a person traveling by foot, traditionally the distance measurement was computed by counting steps then multiplying the number of steps by the individuals average step length. This navigation system, however, is highly prone to errors, which when compounded can lead to highly inaccurate position and distance estimates.
An example of a more advanced navigation system is an inertial navigation system (INS). The basic INS consists of gyroscopes, accelerometers, a navigation computer, and a clock. Gyroscopes are instruments that sense angular rate. They are used to give the orientation of an object (for example: angles of roll, pitch, and yaw of an airplane). Accelerometers sense a linear change in rate (acceleration) along a given axis. Inertial navigation systems are particularly useful for an application where the trajectory of the vehicle or person does not maintain a fixed course or speed while traveling (i.e. high dynamics).
In one implementation of this embodiment, three mutually orthogonal gyroscopes and three mutually orthogonal accelerometers provide sensor data to the inertial navigation system. This accelerometer configuration provides three orthogonal acceleration components which can be vectorially summed. Combining the gyroscope-sensed orientation information with the summed accelerometer outputs yields the INS's total acceleration in 3D space. At each time-step of the system's clock, the navigation computer time integrates this quantity once to get the body's velocity vector. The velocity vector is then time integrated, yielding the position vector. These steps are continuously iterated throughout the navigation process.
Dead reckoning techniques can provide a better long-term solution; however, for best performance, these techniques require motion that is predictable (i.e., nearly constant step size and in a fixed direction relative to body orientation). Integrating traditional inertial navigation and dead reckoning techniques offers a solution to achieve optimal geographic location performance in the absence of GPS or other radio-frequency positioning aids.
Global Positioning System (GPS) is one of the most recent developments in navigation technology. GPS provides highly accurate estimates of position and distance traveled. GPS uses satellites to transmit signals to receivers on the ground. Each GPS satellite transmits data that indicates its location and the current time. All GPS satellites synchronize operations so that these repeating signals are transmitted at the same instant. The signals, moving at the speed of light, arrive at a GPS receiver at slightly different times because some satellites are farther away than others. The distance to the GPS satellites can be determined by estimating the amount of time it takes for their signals to reach the receiver. When the receiver estimates the distance to at least four GPS satellites, it can calculate its position in three dimensions.
When available, positioning aids such as GPS control navigation error growth. GPS receivers, however, require an unobstructed view of the sky, so they are used only outdoors and they often do not perform well within forested areas or near tall buildings. In these situations, an individual using a GPS is without an estimate speed and position.
The U.S. Pat. No. 6,522,266 entitled “NAVIGATION SYSTEM, METHOD AND SOFTWARE FOR FOOT TRAVEL” that issued on Feb. 18, 2003 describes a method of handling unusual motions (relative to walking) such as sidestepping, which can cause significant errors if the unusual motion is used for an extended period of time. U.S. Pat. No. 6,522,266 is also referred to here as the “the 266 patent” and is hereby incorporated herein by reference.
A need exists for a personal navigation system that defines and implements a step-time threshold to delineate types of motion, such as walking and running, and that generates and implements model parameters specific for each type of motion in order to provide an individual with estimates of position and distance traveled. It is also desirable for the personal navigation system to integrate the best navigation features of known navigation techniques with the step-time threshold and the model parameters specific for each type of motion regardless of variations in the step length for different types of motion, regardless of variations in the direction of the step, and regardless of the terrain over which they might travel.